John 10:27-28

John 10:27 repeats revelation Jesus had previously given (John 10:3-5; John 10:14). The eternal life that Jesus gives is His own life. Consequently it is impossible for His sheep ever to perish. Their ultimate security rests with the Good Shepherd who promised here that no one would be able to snatch them out of His hand-no thief (John 10:10), no robber (John 10:8), no wolf (John 10:12), no one (cf. Romans 8:35-39). The construction of the Greek clause "they shall never perish," with a double negative, (ou me apolontai eis ton aiona) stresses the impossibility strongly (cf. John 3:16). Jesus had previously said that part of the task that the Father had given Him to do was to preserve all those whom the Father gave Him (John 6:37-40). Thus we can see that it is impossible even for one of the sheep to wriggle out of the Good Shepherd’s grasp.

"We should notice that the teaching of this verse is not that believers will be saved from all earthly disaster, but that they will be saved, no matter what earthly disaster may befall them." [Note: Morris, p. 463.]

This is one of the clearest promises of the eternal security of the believer that God has given us in His Word. It is also a clear statement of the fact that eternal life comes to us as a gift, not as wages we earn (cf. Ephesians 2:8-9).